1. Field of the Invention
The present invention relates to a magnetic head slider for a magnetic disk device and also to a magnetic disk device, and more particularly to a magnetic head slider of a low flying height-type for achieving high reliability and high-density recording and also to a magnetic disk device having such a magnetic head slider.
2. Description of the Related Art
In magnetic disk devices, attempts have now been made to achieve a low flying height design of a slider and also to stabilize a flying height.
For example, as disclosed in JP-A-6-325530, there has been proposed a slider in which a surface (step surface) structured by a step extending in a recessing direction from a flat surface portion of a rail for flying (air bearing rail) is formed at an inflow-side portion of the rail of the slider, and the depth of this step surface (that is, the height of the step) is made microscopic so that a predetermined flying height of the slider can be achieved without depending on the peripheral speed of a disk. In this known example, the rail for flying has the step surface provided at the inflow-side portion, the step, and the flat surface portion extending from this step portion, and the depth of the step surface (that is, the height difference between the step surface and the flat surface portion) is not more than 700 nm, and by doing so, there can be provided the slider which can fly with a predetermined flying height without depending on the peripheral speed of the disk. A slider, having a step of such a microscopic depth (height), will be hereinafter referred to as “microscopic step slider”.
JP-A-7-21717 discloses a slider in which two inflow pads and one outflow pad are provided on the slider, and side edges of the pads are inclined to an angle generally equal to a predicted maximum inclination so that even on a smooth magnetic disk, the slider can be disposed in linear contact with the magnetic disk, thereby preventing the sticking of the slider to the disk.
Further, in order to achieve the above-mentioned low flying height design of the slider, the disk surface is made flat and smooth. The mean surface roughness Ra of a currently-used disk is reduced to not more than 10 nm. There has been adopted a contact start stop system (hereinafter referred to as “CSS system”) in which when the rotation of a magnetic disk is stopped, a slider is held in contact with a disk surface, and when the disk is rotated, the slider flies off the disk surface. In a device using this CSS system, a so-called sticking problem arises from a smooth disk surface, and more specifically, when the rotation of the disk is stopped, the slider sticks to the disk surface. When the slider sticks to the disk, there are encountered troubles such as the failure of the disk to rotate. In order to solve this problem, a slider, in which microscopic projections are formed, on the slider to reduce the area of contact between the slider and the disk, is disclosed in JP-A-4-28070 and JP-A-9-245451.
In a microscopic step slider as disclosed in the above JP-A-6-325530, a sticking problems arises from a smooth disk surface. In order to avoid this sticking problem, even if microscopic projections as disclosed in JP-A-4-28070 and JP-A-9-245451 are provided on a rear portion or front and rear portions of the flying rail, or a negative-pressure pocket thereof, the following problems are encountered:
(1) If the flying rail of the slider or the microscopic projection is brought into contact with the disk surface for some reason at the time of CSS or during the flying of the slider over the rotating disk, the flying surface (surface facing the disk) of the slider is pulled by a frictional force, so that the slider is turned or angularly moved about a pivot (load-acting point) of a suspension to lean forward, and as a result the front edge of the step surface of the slider is brought into contact with the disk surface. The front edge of the step surface is sharp, and when this front edge is brought into contact with the disk surface, there arises a problem that the disk is damaged by this front edge. Particularly in a magnetic disk device of the type in which the flying height of the slider is small, and the smooth disk is used for the purpose of achieving a low flying height, this problem is serious because of the large frictional force. Therefore, to prevent the slider from leaning forward so that the front edge will not brought into contact with the disk surface is an important subject matter for preventing damage to the disk and for securing the reliability, One method of overcoming this problem is to chamfer the front edge of the step surface (to provide a curvature) to increase the contact area, thereby reducing a contact stress (load pressure). With this method, however, an opening of the step surface (that is, the distance of the step surface from the disk surface) is large, and an increased amount of dust and dirt enter this opening, which leads to a possibility that the flying height is varied. When the flying height is thus varied, an error in the data reading and writing operation occurs. Therefore, this method is not effective in preventing the damage of the disk by the front edge (sharp edge portion) of the step surface.
(2) Another main factor in the variation of the flying height of the slider is a reduction of the atmosphere pressure. More specifically, when the magnetic disk device is used at a place of a high altitude, the pressure of the atmosphere is low, so that the flying height is reduced. When the flying height is reduced, there arises a problem that the slider comes into contact with the disk to damage the same. To reduce the amount of reduction of the flying height of the slider due to the decrease of the atmospheric pressure is an important subject matter for achieving the low flying height design of the slider and also for preventing the contact of the slider with the disk so as to secure the reliability.
And besides, when the microscopic projection is provided on the rail of the slider, the reduction of the flying height is, in some cases, limited depending on the height of this projection, so that there is a case that the low flying height design can not be achieved.